A known drive system for a hybrid vehicle is disclosed in JP2011-109839A (hereinafter referred to as Patent reference 1). The drive system disclosed in Patent reference 1 is provided with an electric motor, an input hub to which an engine drive force is transmitted, an output hub which is rotatably connected to an axle, and a clutch device to connect and disconnect the input hub to the output hub. This configuration allows a hybrid vehicle to run only by the electric motor, to use an engine and the electric motor at a same time as power sources when a large drive force is needed, and furthermore, to cause the electric motor to generate electricity by using an engine rotation.
As heavy members, for example, clutch plates, a piston and a coil spring to press the clutch plates, and a rotor of the electric motor are mounted to the aforementioned output hub, a huge load is applied on a bearing on which the output hub is journaled. Thus, according to the known drive system for the hybrid vehicle, the output hub is journaled on the case by a multiple-row angular contact ball bearing to restrain a core vibration of the output hub at a time of a rotation.
However, in a structure where the output hub is journaled on the case by the multiple-row angular contact ball bearing, as a distance between balls of the multiple-row angular contact ball bearing is short, and the output hub is supported by a single angular contact ball bearing at one side, the core vibration of the output hub when the output hub rotates in a high speed is not restrained enough.
A need thus exists for a drive system for a hybrid vehicle which is not susceptible to the drawback mentioned.